Bai W, Rowan B G, Allgood V E, O'Malley B W, Weigel N L
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
J Biol Chem. 1997 Apr 18;272(16):10457-63. doi: 10.1074/jbc.272.16.10457.
Many steroid receptors, including chicken progesterone receptor, have been shown to be activated in the absence of their cognate ligands by modulators of kinases and phosphatases. To investigate the molecular mechanism of ligand-independent activation, chicken progesterone receptor mutants in which either one or all four of the previously identified phosphorylation sites have been changed to nonphosphorylatable alanine were analyzed for their ability to be activated by progesterone, 8-bromoadenosine 3':5'-cyclic monophosphate, or a dopamine agonist, SKF82958. Our current study shows that the receptor is differently phosphorylated in ligand-dependent and ligand-independent activation. The transcriptional activity of the receptor in response to 8-bromoadenosine 3':5'-cyclic monophosphate is affected by mutation of either Ser211 or Ser260. In addition, our data demonstrated that none of the four sites is absolutely required for the activation of the receptor by either 8-bromoadenosine 3':5'-cyclic monophosphate or the dopamine agonist. Treatment with 8-bromoadenosine 3':5'-cyclic monophosphate did not increase the overall level of receptor phosphorylation or cause phosphorylation of the receptor at alternate sites. These data raise the possibility that ligand-independent activation of the chicken progesterone receptor may be mediated through changes in the phosphorylation of coregulators or other protein factors interacting with the receptors.
包括鸡孕酮受体在内的许多类固醇受体，已被证明在缺乏其同源配体的情况下会被激酶和磷酸酶调节剂激活。为了研究非配体依赖性激活的分子机制，对鸡孕酮受体突变体进行了分析，这些突变体中先前确定的一个或所有四个磷酸化位点已被改变为不可磷酸化的丙氨酸，以检测它们被孕酮、8-溴腺苷3':5'-环磷酸单酯或多巴胺激动剂SKF82958激活的能力。我们目前的研究表明，该受体在配体依赖性和非配体依赖性激活中磷酸化方式不同。受体对8-溴腺苷3':5'-环磷酸单酯的转录活性受Ser211或Ser260突变的影响。此外，我们的数据表明，这四个位点中没有一个对于8-溴腺苷3':5'-环磷酸单酯或多巴胺激动剂激活受体是绝对必需的。用8-溴腺苷3':5'-环磷酸单酯处理不会增加受体磷酸化的总体水平，也不会导致受体在其他位点磷酸化。这些数据增加了一种可能性，即鸡孕酮受体的非配体依赖性激活可能是通过共调节因子或与受体相互作用的其他蛋白质因子磷酸化的变化来介导的。
